Stuck O2 Sensor? How?
 

SES light came on, went off over a few days. I know that's more or less EVAP issues so I don't panic. Scanned and got some interesting codes:
P0140: O2 sensor circuit No activity, Bank 1,Sens 2 . Days later this code,
P2270: O2 sensor Signal Stuck, lean bank 1 , Sen 2. Cleared, days later again.
I took pics of additional readings while running, but nothing else stated issues with O2 that I could understand.
Is Bank 1 the front 3 cylinders from radiator back? Is Sen 2 post cat?
Gas mileage is what it's been for months. Now using reg 87 oct gas.
It's a 250K miles 01-3.0 auto setup.
I'm guessing it's not that serious.
Thanks:dunno:

87? Ouch. Sensor 2 is the rear sensor. You should scan it with a BMW capable code reader. P codes are okay but can sometimes not be all that helpful on BMWs.

Ok, gotta find one. Yeah, 87, it's cheap, around town for an older beast. Runs smooth, no issues, I do throw in gas treatments now n then. Getting 18-19 mpg mixed use. BTW, not a lot of highway speed driving these days as a daily. First 240K were 91 or better though.

I'd at least go mid-range on the octane rating and stick with a top tier fuel such as Shell or Exxon. Avoid additives in my opinion as they can contribute to shorter sensor and catalyst life. My original O2 sensors lasted 260,000 miles, the second set went 106,000 miles but my driving shifted towards more city driving.


I stick with Shell premium and don't use any additives. My spark plugs always last more than 100,000 miles and I am still on the original cats.


2002 X5 3.0 368,600 miles
2014 428i 65,500 miles


2004 325i sold at 123,600 miles
2001 325i sold at 66,000


1970 Firebird under restoration

Similar here, orig cats. O2's went 170K, on second set. Always used 91oct up to about 15K miles ago. Wow, that's serious mileage. What else is original?

Also, yes, bank 1 is cylinders 1-2-3, which are the front 3.

Good thinking to doubt the sensors / wiring first, rather than the engine / ECU / cat.

I'd at least get under there to look at things. Maybe a connector is compromised.

Simple test would be to swap sensors and see if/where the codes move. Sometimes that is not so easy due to corrosion. So an alternative would be to swap the connections, which are up in the engine bay, under the plastic cover, on top of the intake manifold, next to the fuel rail. Here's a pic of them. One is clear. The other is there too, held up by my middle finger. Like the O2 sensors themselves, the connectors are interchangeable. Based on the wire bends and lengths of wires, it is easy to avoid mixing them up when reinstalling.
Attachment 76961

And in case it is not clear, that is looking rearward at the engine. My left hand there is on the right / starboard side of the engine. Intake manifold is slightly lifted clear. The connector has been removed from its clip seen there on top of the fuel rail.

I'm pretty sure it should be easily accessible after removing the plastic covers on top of the engine.

87??? Hopefully your knock sensors are good. That get up and go with a BMW just got up and went.

Transmission fluid
A/C system has never been opened.
Brake system has never been opened - only flushed.
Rear axle CV boots are original
No internal engine issues - original VANOS.
No measurable stretch or wear on timing chains at 242,000 miles.
Original fuel injectors


Replaced once:
Rotors, alternator, radiator, front axles (PO drove with cracked boots), 4 coils, front drive shaft & transfer case, suspension bushings, front tension struts, upper rear control arms, differential seals, DISA, steering angle sensor, valve cover and fuel pump.


2002 X5 3.0 368,600 miles
2014 428i 65,500 miles


2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles


1970 Firebird under restoration

Original Dvanos? That's quiet amazing since the BMW Oems were junk. But hey, way to go. I too had to do front axles, but nothing else. Of course the front end suspension components are less than substantial so I have done those 1 x. Rear is orig. Drivetrain orig. minus guibos. Fluid/filter trans every 60-70K with transfer case. Belts, upper hose, w.pump,thermo, orig A/C , replace alternator at 200K. Orig radiator,new bottle. Just rebuilt the rear license plate lights. New taillamps. FSR 1x, but need a CControl module, replaced CCV at 175K. Basically a great ride to this day. Bought with 33K for $30K. So, it's been a good deal. Oh, engine mounts from sitting 6months.

Post cat sensors only used for emission monitoring. I would recommend getting them replaced sooner than later though